Oxirane reactions deoxygenation

The pyrazine I reacts with singlet oxygen to yield the endoperoxide 2, which is converted into the 1,3,6-oxadiazepine 4 on treatment with triphenylphosphanc. It is thought that the reaction involves deoxygenation to the bicyclic oxirane 3 as the key intermediate.320... 

Dichlorocarbene reacts with oxiranes to produce dichlorocyclopropanes [18] via an initial deoxygenation reaction (Scheme 7.22). 

Epoxides (oxiranes) can be reduced in different ways. So-called deoxygenation converts epoxides to alkenes. Such a reaction is very useful since it is the reversal of epoxidation of alkenes, and since both these reactions combined represent temporary protection of a double bond. 

Action of LTBH upon the 2,2 -ditosylate 94 afforded the known 3,3 -dideoxy sugar 100 less efficaceously, evidently because of competing, partial 0-desulfonylation which, however, provided as a benefit the new, unsymmetrical disaccharides 1Q2 and 103 (11 and 8%) that were formed via the monoepoxide 101. Compound 1Q2 was the main product of deoxygenation when the 2-monotosylato 95 was treated with LTBH, although anti-FUrst—Plattner opening of intermediary oxirane 101 is believed to have taken place as a minor side-reaction in this instance. 

The deoxygenation of ethers by C atoms was first studied by McKay and Wolfgang who reported a high yield of in the reaction of with oxirane. Deoxygenation of oxrranes was subsequently reported for both arc and chemically... 

These reactions can be carried out catalytically because the tellurium precipitated during the deoxygenation of the oxiranes will react rapidly with added sodium diethyl phosphite. Lithium 0,0-diethyl tellurolophosphate is a more powerful deoxygenation reagent and is able to convert certain internal epoxides to olefins in a stereospecific manner3. 

Another possibility in the method is the reaction via a 3-hydroxydiphenylphosphine oxide. Deoxygenation takes plaee with retention by means of triphenylphosphine derivatives ArsP=X (X = S, Se). (Eq. 103). Triphenylphosphine itself has often been employed in deoxygenation of oxiranes and thiiranes. 

If use is made of the five-membered cyclic phosphorus derivatives, the geometry of which is more suitable than that of the triphenylphosphine, formation of the phos-phorane intermediate is more favored and the yield of olefin increases. Deoxygenation with KSeCN in mildly alkaline medium can similarly occur by heteroatom exchange retention is observed as a consequence of double inversion. Open-chain compounds react with good yields, but cyclic oxiranes yields vary considerably with the number of ring atoms, due to steric hindrance. Alkali metal 0,0-diethyl-phosphorotellurates are very useful reagents for the conversion of terminal oxiranes, Eq. 104 but the reaction does work for other types. In the case of oxiranes formally derived from acyclic olefins, the (Z) compounds react more readily than the (E)-oxiranes. ... 

For the one-step conversion of oxiranes to alkenes a variety of reducing metals have been used, including Li, Ti°, low-valent Nb, Cr , and Sm . ° In the latter case, HMPA and N,N-dimethylami-noethanol facilitate the reaction. Reaction of 2 equiv. of Bu"Li with WCle produces a reagent which effects efficient deoxygenation of oxiranes, as exemplified in equation (8). This reagent is particularly valuable for the deoxygenation of tri- and tetra-substituted oxiranes and is compatible with ethers and esters, although aldehydes and ketones reductively couple with it. 

A fragmentation reaction, triggered by the formation of an oxiranylcarbinyl radical resulted in the deoxygenation of a spirocyclic oxirane (Scheme 47) (95TL19). 

Thermally labile telluriranes can also be generated from oxiranes by treatment with sodium 0,0-diethyl phosphorotelluroate, and this reaction was especially applied to the selective deoxygenation of terminal epoxides (see Section 1.07.6.2). 

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